1. Field of the Invention
The invention relates to ethylene-vinyl acetate copolymer (hereinafter referred to as EVAc) hot-melt adhesives and more particularly relates to such adhesives having extended molten stability and to methods of their preparation.
2. Brief Description of the Prior Art
EVAc-based hot-melt adhesives, their preparation and methods of use are well known in the art; see for example U.S. Pat. No. 3,560,420. These adhesives compositions are used extensively in packaging, laminating and bookbinding. However, their use in typical application apparatus is impaired by the tendency of these hot-melt adhesive compositions to exhibit relatively short pot-lives; i.e.; fluid stability under molten conditions. Generally viscosity increases or gelation and a "skinning" over of air exposed surfaces occurs within relatively short periods of time after initial melting. Almost all EVAc adhesives contain a thermoplastic, modifying resin as a major component which is known as a tackifier. Tackifiers increase the adhesion and lower the viscosity of hot-melt adhesives. The improvement in adhesion is believed to be a result of improved wetting.
The method of the invention is advantageous in that it significantly increases the hot melt stability of EVAc-based hot-melt adhesives. This permits an operator to employ apparatus with a greater time latitude and to melt the adhesive compositions well in advance of its application. This provides more flexibility in use of the adhesives.